1. Field of the Disclosure
The present disclosure relates to a wireless communication apparatus, and in particular to an ESD protection device that protects a power amplifier used in a wireless communication apparatus, and specifically in a transmission circuit thereof, from electrostatic discharge (ESD).
2. Description of Related Art
Semiconductor devices used in a variety of electronic devices are known to operate erroneously or be broken because of noise (ESD noise) due to electrostatic discharge occurring inside or outside the electronic device.
In wireless communication apparatuses having an antenna, such as cellular phone terminals which have become widespread in recent years, in particular, ESD noise may be picked up by the antenna or an antenna line (antenna path) to significantly affect semiconductor devices forming a power amplifier connected to the antenna.
As measures against ESD, the following methods are used in the related art.
a) Voltage limiting elements such as a varistor, a Zener diode, and a suppressor are disposed for input and output pins of the semiconductor devices to protect the semiconductor devices by cutting off a high voltage due to ESD by causing such a voltage to bypass the semiconductor devices in the case where an overvoltage such as ESD noise is applied.
b) An inductor (shunt L) or the like is provided to connect the antenna line to GND to cause a DC component to flow to GND by bypassing the semiconductor devices, or a capacitor (series C) or the like is connected in series with the antenna line to prevent a DC component from passing through the semiconductor devices.
The above method a) may be effective measures against a high voltage that may cause a device breakage. However, the impedance of the antenna line may be varied in accordance with the electrical state around the antenna, which may cut off a voltage for a transmission output to result in distortion in transmission output. In particular, the antenna impedance of the cellular phone terminals is significantly variable because of inconstant environments, and is highly likely to be problematic.
Of the method b), the method in which the antenna line is connected to GND in terms of DC using the shunt L can effectively eliminate the effect of ESD noise at a frequency that is sufficiently low with respect to the transmission/reception frequency. However, ESD noise is distributed over a significantly wide frequency domain, and thus the effect of ESD noise cannot be completely eliminated.
Likewise, the method in which the antenna line is separated from the semiconductor devices in terms of DC using the series C can effectively eliminate the effect of ESD noise at a frequency that is sufficiently low with respect to the transmission/reception frequency.
However, ESD noise is distributed over a significantly wide frequency domain, and therefore the effect of ESD noise cannot be completely eliminated by the methods according to the related art discussed above.
In recent years, in particular, tolerance to ESD noise has been decreasing along with miniaturization of integrated circuits and size and weight reduction of devices, and there is an increasing need for more effective ESD measures.